1. Field of the Invention
The present invention relates to a high power flip chip LED, more particularly, which can prevent the current channeling to increase the luminous area while equalizing the current density across the luminous area thereby generating high brightness light.
2. Description of the Related Art
A Light Emitting Diode (LED) basically consists of a junction of p- and n-doped semiconductor layers formed on a sapphire substrate as a kind of optoelectric device. When applied with electric current, the LED generates light converted from a predetermined level of energy corresponding to its band gap through the electron-hole re-combination.
People have become familiar with LEDs of this type as they are adopted in displays of general electronic instruments. Although early stage LEDs were limited in the brightness and color, various high brightness LEDs are produced at present according to advanced materials and improved manufacturing technologies, emitting full colors of lights including white light in the visible band. The LEDs of high brightness, high efficiency and various colors are being widely utilized in many countries for various displays such as a large-sized electronic display board, an exit lamp, a traffic lamp and a vehicle lamp. The LEDs are expected to be applied to wider fields in the future since they are small, light and endurable while having a long lifetime.
The color emitted from an LED is determined by the component of its semiconductor material. Common examples of the semiconductor material for LEDs include ZnSe, nitrides such as GaN, InN and AlN and nitride compounds containing nitrides mixed at certain contents. In particular, GaN is most widely used.
The growth of GaN crystal is generally carried out via the Metal Organic Chemical Vapor Deposition (MOCVD). The MOCVD typically flows organic compound reactant gas into a reactor at a temperature of about 700 to 1200° C. to grow an epitaxial layer on a substrate, which is generally made of sapphire (Al2O3) or Silicon Carbide (SiC). For the purpose of promoting fine crystal growth, a low temperature buffer layer is formed between the substrate and the nitride layer at a thickness of about 20 to 30 nm to prevent the stress originated from the lattice constant mismatch in the growth of the nitride or epitaxial layer on the sapphire or SiC substrate.
As applied to various fields, and more particularly, to illuminators, present LEDs are required to have higher brightness, larger chip dimension and larger luminous area. Accordingly, various flip chip structures have been developed to realize larger luminous area as well as higher brightness.
FIG. 1. illustrates an example of a flip chip LED disclosed in the U.S. Pat. No. 6,573,537. Referring to FIG. 1, an n-doped epitaxial layer or n-doped semiconductor layer 11 is formed on a transparent substrate or superstrate 10, and a p-doped semiconductor layer (not shown) is formed on a first or major region of the n-doped semiconductor layer 11. A p-electrode 20 is formed on a first or major region of the p-doped semiconductor layer, and an-electrode 22 is formed on a second or minor region of the n-doped semiconductor layer 11 and a second or minor region of the p-doped semiconductor layer. The electrodes 20 and 22 are connected with a power supply via conductive contacts 41. The n-electrode 22 is in the form of fingers interposing the p-electrode to prevent current channeling.
However, the above LED structure of the prior art has the following drawbacks. That is, the thin fingers of the p-electrode 22 are extended interposing the wide p-electrode 22, and supplied with current via the conductive contacts 41 disposed at lower ends of the p-electrode fingers. In this circumstance, because the p-electrode fingers are very thin, the current density applied to upper ends of the p-electrode fingers is smaller than that applied to lower ends thereof. This makes the current density across the LED ununiform and also the emission ununiform.
In order to solve this drawback, there was proposed a structure that conductive contacts are disposed at both ends of p-electrode fingers. However, this structure also fails to sufficiently solve the ununiformity of the current density across the LED.